do you think partition was a bad idea?
A very tough question, we don't know how it would have been if we were together, but we can safely say that it would have been great if we had ONLY sane & mature people on all sides (I am talking about all 3 countries).
You can see India as a big united country has greater influence in the world, we could achieve more in science & technology because of higher available resources; both in terms of money and talent, and going forward we will continue to become more and more important in global arena. Size does matter, Singapore can never have the kind influence China enjoys.
So we can say that together we would have been an even bigger country, with greater resources, greater achievements, and greater importance around the world. And if all parts of India can get along very well with each other, then we would have gotten along very well with Bengalis of Bangladesh and Punjabis, Sindhis, Balochis, of Pakistan also. But only if..............!!
Also look at the kind of money and energy we have spent against each other, all the war, insurgency, dirty politics, all would not have happened if we were one proud nation.
But, all this would have happened ONLY IF we were not so blinded by our religious identities that we couldn't even live with each other.
There was a reason behind the separation, who knows whether the hatred among some sections of Hindus & Muslims would not turn our country into world's biggest civil war zone? Then we wouldn't even achieve what we have achieved separately, it is better to live separately and happily, than to live together and keep fighting over religion.